Applying Sales Tax to an invoice after it has been posted.

SOLVED

I was wondering if there was a way to apply sales tax to an invoice after it has been processed.  The invoice was paid via a CC. The customer was set up accidently as 'exempt'. So invoice is already paid. Customer said to charge the sales tax to same CC but I don't know how to 'fix it'....Please help if possible.  I know I can't 're-do' it b/c of the CC being charged again. Just need to get the sales tax applied and in the system.

 

Thank you.